1. Field of the Invention
This invention pertains generally to electrical power supply circuitry, and more particularly to a method and apparatus for obtaining multiple, independent, variable voltage power supplies from a single secondary transformer winding.
2. Description of the Background Art
There exists situations wherein two or more independently variable voltage DC power supplies are required; for example, the operation of multiple direct current devices such as DC servo motors or DC stepper motors in motion control and robotic applications. While it is possible to link together multiple linear power supplies or multiple switching power supplies under a common control system, there are a number of problems with doing so, including: (i) it is difficult and expensive to link together, in a coordinated manner, the control of such power supply combinations; and (ii) both types of such power supplies require numerous components that take up a large amount of physical space and are costly to build. Since physical transformers are not ideal devices, an increase in current draw will cause a lowering of the output voltage on the secondary winding (and on any other secondaries that may be on the same transformer). The result is that the power supply output capacitors may not get the desired amount of current and voltage (i.e. there is excessive voltage sag on the transformer), and instabilities can arise as the various instances attempt to compensate by drawing even more current on subsequent cycles.